The present invention generally relates to an apparatus and method for sensing the presence and position of an object including an occupant within a motor vehicle. More specifically the present invention relates to a system using one or more reflective capacitive proximity sensors whose electric field is modified by the presence of the object.
Various technologies have been proposed to sense the presence and position of occupants or other objects in a motor vehicle. These prior systems include infra-red and ultra-sonic transmitters and receivers which generate and receive reflected waves. Capacitive proximity sensors have been used in a variety of applications as switches, occupant and intrusion sensors. U.S. Pat. No. 3,943,376 shows one such capacitive sensor used in the vehicle to sense the presence of an occupant. One plate of a capacitor is embedded within the vehicle seat and another plate is positioned elsewhere within the vehicle such that the electric field extends therebetween. Changes in capacitance are affected when the occupant sits between the two plates changing the effective dielectric constant of the capacitor. U.S. Pat. No. 5,166,679 shows a capacitive object intrusion sensor. This type of capacitive sensor has been called a "capaciflector" or reflective capacitor. This sensor was originally developed for use in outer space and designed to be mounted on a robot arm to sense the closeness between the robot arm and an object.
The primary purpose of the present invention is to provide a system and method to sense the position and to detect the presence of one or more objects such as child seat and/or occupants within a passenger compartment of a motor vehicle. Once having detected the presence of an occupant and its position the dynamic performance of various safety restraint components in the vehicle, e.g., airbags, pretensioner for seat belts can be tailored or matched to the occupant's seating position and severity of an accident. As will be seen from the description below, changes in the generated electric field are analyzed to provide information for example on a) the presence of an object or occupant, b) the type of object present (e.g. an infant seat installed facing forward or rearward) and c) the size of an object or occupant in the passenger compartment.
One embodiment of the invention comprises a forward positioned first reflective capacitive sensing element installed in, at or near each air bag deployment door. Typically these doors are located on the steering wheel, as part of a driver air bag module, and on or in the instrument panel as part of a passenger side air bag module. Depending upon the depth of the electric field of this occupant sensor it can be used to sense both a normally seated occupant or an out-of-position occupant. To sense only out-of-position conditions, the depth of the field produced by the first capacitive sensor is chosen so that it does not interact with a normally seated occupant but is modified when the occupant is out of position such as when the occupant is too close to the steering wheel or instrument panel. When used as described this sensor configuration cannot distinguish if the occupant is not seated. If needed the sensor output can be supplemented by using a buckle sensor which when closed would normally indicate that an occupant has seated himself and has buckled the seat belt about him. This single occupant sensor can also be used to generate information about the normally seated occupant. In this situation, the field extends beyond the normal seating position such that when an occupant is seated the sensor generates a first output signal. As the occupant moves closer to the location of the sensor its output signal varies to indicate that the occupant or other object is now much closer to the sensor, i.e. out of its normal position. Another embodiment of the invention uses two reflective capacitive sensors. The first capacitive sensor is installed as related above having a field depth which does not extend to the occupant. A second capacitive sensor is installed in or on each side door panel. As can be appreciated the second sensor provides a positive indication of whether or not the object/occupant is properly seated in the vehicle seat and out-of-position information is generated by the first sensor. The exact size, location and quantity of the reflective capacitive sensor used is dependent on vehicle geometry, packaging restrictions and the particular sensing resolution desired. Various combinations of reflective capacitance sensors may be positioned throughout the vehicle to measure the positioned and presence of other objects within the passenger compartment of the vehicle. A third system option can be achieved by having the fields produced by the forward occupant sensor and the door mounted sensor interact. In this manner both sensors can generate a signal indicative of the normally seated occupant and provide some degree of redunancy.
It is an object of the present invention to provide a system to sense occupant/object presence and to modify the operating characteristics, as applicable, of various components of a safety restraint system such as an air bag and/or seat belt pretensioner.
Accordingly the invention comprises: a system for sensing the presence of an object within a vehicle's passenger compartment including an occupant in a motor vehicle comprising: safety restraint means, such as a system including a three point seat belt system having a pretensioner and various air bags for protecting the occupant during a crash, actuating means for activating corresponding safety restraint means during a collision; first occupant sensing means fixedly positioned in the vehicle for generating an electric field in the passenger compartment and for generating an output signal indicative of occupant presence or lack thereof, wherein the presence of an object affects the electric field causing a change in the output signal of the sensing means; the sensing means mounted on one of a vehicle's steering wheel assembly, or instrument panel or headliner for driver position detection or the instrument panel, near the passenger air bag module, or other vehicle location adequate for passenger position detection. The systems may also include crash sensor means sensor coupled to an electronic control means for sensing an actual or impending crash and for generating an output signal indicative thereof. The electronic control means is reactive to a combination of the output signals from the crash sensor means and occupant sensor means for determining whether or not to generate a signal to activate the safety restraint means and if it is necessary to modify its operating characteristics if for example the occupant is out of position.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.